Uncertainty and variability of infiltration at Yucca Mountain: Part 1. Numerical model development

• Published in: Water resources research 2013-06, Vol.49 (6), p.3787-3803
• Main Author: Stothoff, Stuart A.
• Format: Article
• Language: English
• Subjects: Aeration zone; Boundary conditions; Infiltration; Mathematical models; modeling; Monte Carlo simulation; Overland flow; Performance assessment; Scale models; Soil infiltration; Soils; Yucca Mountain
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/wrcr.20252

The U.S. Nuclear Regulatory Commission investigated climate and infiltration at Yucca Mountain to (i) understand important controls and uncertainties influencing percolation through the unsaturated zone on multimillennial time scales and (ii) provide flux boundary conditions for up to 1 million years in performance assessment models of the proposed Yucca Mountain repository. This first part of a two‐part series describes a procedure for ing the results from detailed numerical simulations of local‐scale infiltration into a site‐scale model considering uncertainty and variability in distributed net infiltration. Part 2 describes site‐scale model results and corroboration. A detailed one‐dimensional numerical model was used to estimate bare‐soil net infiltration at the scales of hours and meters for 442 soil, bedrock, and climate combinations. The set of results are ed into three parametric response functions for decadal‐average bare‐soil infiltration given hydraulic and climatic parameters. The three ions describe deep soil, shallow soil over a coarser layer, and shallow soil over a finer layer. The site‐scale model considers spatial variability and uncertainty of the input parameters on a 30 m grid, using the ions independently in each cell. Two additional ions account for overland flow and vegetation. The model uses Monte Carlo simulation, with all input parameters uncertain and spatially variable, to calculate the mean and standard deviation of net infiltration in each grid cell for selected climate states. Using ions rather than detailed simulations speeds calculation of infiltration realizations by many orders of magnitude relative to a detailed simulation. Key Points 1D simulations provide time-averaged net infiltration. Three response functions are developed. The ions are used in Monte Carlo simulation.